Large depth filters of layers of particulate material are used to remove turbidity from water and the like. For example, the Culligan International Company of Northbrook, Ill. offers Models HQ20, HQ24, and HQ30 depth filters capable of purifying water at flow rates ranging from 50 gallons per minute to 120 gallons per minute.
While depth filters such as these are very effective for their purpose, they do exhibit the disadvantage of being of heavy weight. For example, the U.S. Army makes use of a Reverse Osmosis Water Producing Unit which incorporates a standard particulate depth filter weighing between 2100 and 2200 pounds. Such a heavy weight obviously has a significant influence on the transportability of such Reverse Osmosis Water Producing Units, particularly their air-transportability.
One reason that such large depth filters must be so heavy is that the various layers of particulate material must be of generally increasing density from top to bottom, to permit them to restratify after back washing, which is the periodic process used to remove collected filter residue from the filter. Accordingly, the lower portions of particulate material in conventional depth filters are relatively heavy.
In accordance with this invention, a depth filter is provided which can be of a weight down to one-half of the weight of corresponding conventional depth filters, while exhibiting performance which is quite comparable to that of the heavier depth filters.